There has been a tremendous increase in the use of nutraceuticals by health consumers for the treatment and prevention of a variety of medical conditions. However, there is very little information in the scientific literature regarding the efficacy and safety of these naturally occurring substances. The overall long-term objectives of the proposed research are: 1) to enhance our understanding of the mechanism of action of nutraceuticals; 2) to determine whether the use of nutraceuticals is associated with adverse effects; and 3) to elucidate the biochemical and molecular mechanisms by which the concurrent use of a nutraceutical and a drug lead to drug interactions. The ultimate aim of this research is to provide a scientific basis for the rational and safe use of nutraceutical products. Therefore, the proposed research has direct relevance to human health. The proposed experiments in the present application is to investigate the effect of ginsenosides on human CYP enzymes which are important catalysts in drug biotransformation and procarcinogen activation. Specifically, the proposed experiments will test the hypotheses that ginsenosides: 1) suppresses the inducibility of CYP1A1 and CYP1B1; 2) inhibits the catalytic activity of CYP1A1, CYP1A2, and CYP1B1; 3) inhibits the hepatic microsomal metabolism of drugs catalyzed by CYP1A2; and 4) inhibits the catalytic activity of CYP3A4 and CYP3A5. These studies will be performed in vitro by employing recombinant cytochrome P450 enzymes, human liver microsomes, and cell culture models (i.e., MCF-7 human breast carcinoma cells) of cytochrome P450.